Project scope is a conceptual thing describing the boundaries of your project, covering what the project encompasses and (maybe more importantly) what it does not encompass. From PMBOK 4:
> **Project Scope**. The work that must be performed to deliver a product, service, or result with the specified features and functions.
Project charters are baselined documents used to capture the agreed-upon objective, scope, benefits, costs, milestones, governance, quality standards, etc etc etc of your project. From PMBOK 4:
> **Project Charter** [Output/input]. A document issued by the project initiator or sponsor that formally authorizes the existence of a project, and provides the project manager with the authority to apply organizational resources to project activities.